The invention relates to an image sensor and display device, and more particularly to an image sensor and display device available to various size pixels of image sensors by compensation of image stress of image signals and subsequent display.
The image sensor has a plurality of unit pixels aligned in matrix within an active image area having a predetermined screen ratio. Each of the unit pixels performs a photo-electric conversion to generate image signals for sequential reading out operations and subsequent transfer thereof to the display device with a predetermined screen ratio. The screen ratio of a vertical length to a horizontal length of the active image area is 3:4 in the NTSC and PAL regulations, while in the high definition television system the screen ratio is 9:16. Namely, the optical image informations are converted to the image signals by the image sensor with a predetermined vertical-to-horizontal ratio of the active image area on which the pixels are aligned in matrix. The image signals are transferred to the display device for display on various sizes of the regulated screens as described above.
In the high definition television system, the display screen comprises an active image area having a vertical-to-horizontal ratio of 9:16 and having scanning line numbers of 1036 in which the scanning lines run in the horizontal direction as illustrated in FIG. 1. The one time scanning on all the scanning lines are carried out in a time of 1/30 seconds for the two-dimensional display. The screen comprises an interlace scanning of A and B fields. The active image are defined by a vertical scanning period and a horizontal scanning period. Inactive area outside the active image area but on the screen comprises a L-shaped area defined by a vertical retrace line period of 89 scanning lines and a horizontal retrace line period as illustrated in FIG. 1. For example, the active image area has a vertical size of 7.9 mm and a horizontal size of 14.0 mm for the alignment of the plurality of unit pixels. In use of the solid state image sensors, 2,000,000 pixels are aligned in such a matrix that 1036 pixels are aligned in the vertical direction and 1920 pixels are aligned in the horizontal direction wherein each pixel has a size of 7.6.times.7.3 micrometers. In case of 1,300,000 pixels being aligned, 1035 pixels are aligned in the vertical direction and 1258 pixels are aligned in the horizontal direction wherein each pixel has a size of 7.61.times.13.56 micrometers. Under the high definition television system, each pixel is rectangular-shaped, but not square-shaped. Similarly, under the NTSC or PAL regulation, high definition television system, each pixel is rectangular-shaped, but not square-shaped. In case of a lens format of 1/2 inches, 250,000 pixels, 330,000 pixels and 380,000 pixels are used wherein unit pixels have the same vertical size but various horizontal sizes to improve a horizontal resolution. Namely, under the conventional image sensor, it is not necessary that the unit pixel is square-shaped. As a large number of the pixels, at a high frequency, the reading out operation for the image signals from the image sensors is carried out. In the solid state image sensor according to the high definition television regulation, 2,000,000 pixels requires 4.25 MHz and 1,300,000 pixels requires 48.6 MHz.
In the high definition television regulation, a single scanning line on the screen is continued to be scanned for 29.6 microseconds. The active image area on the display screen includes 1035 or 1036 scanning lines. The image in the active image area of the solid state image sensor is displayed without any lack of the image. A variation of the frequency for the reading put operation may merely be represented as a variation of the horizontal resolution on the screen.
FIG. 2 illustrates configurations of an image camera 1 and a display device 5. The image camera 1 is provided with a camera lens 2. The image camera 1 includes a solid state image sensor 3, a driving circuit 41 being connected to the solid state image sensor 3 for driving the solid state image sensor 3 and an image signal processor 42 being connected to the solid state image sensor 3 for processing the image signals into which the optical images are converted by the solid state image sensor 3. The image signal processed by the image signal processor is outputted from an output terminal to be inputted into an input terminal of the display device 5. The display device 5 includes a screen section 6 with a cathode ray tube, a horizontal scanning circuit for permitting a horizontal scanning of electron beam on the screen section and a vertical scanning circuit for permitting a vertical scanning of electron beam on the screen section as well as an image signal display circuit for permitting an image signal display on the screen.
In the image camera 1, for every 1/30 seconds image signals corresponding to 1125 scanning times on the screen or 1045 to 1036 scanning lines on the active image area are read out by the solid state image sensor 3 in cooperation with the driving circuit 41 for processing of the image signals and subsequent output from the output terminal of the image camera 1. Thereafter, the image signals are inputted into the input terminal of the display device 5 to be supplied through the display circuit 81 to the screen on which all image informations picked up by the active image area of the solid state image sensor 3 are surely displayed.
Recently, computers tend to process frequently image signals with use of image synthesis or special processing, for example, enlargement or reduction of an image and rotation or turning over of the image. Under this circumstances, the squared pixels involved in the image sensor are suitable.
In the field of printing industry, the enlargement and reduction of the image are used. An improvement in the resolution by the interpolation between the pixels in the digital processing and a color tone compensation are also required. In view of the above, the squared pixels of the solid state image sensor are suitable. In this fields, a high definition image is essential. At present, a one dimensional high definition image input scanner has been realized.
As a two dimensional high definition scanner has been realized for a high definition television system only in which each pixels is rectangular-shaped but not square-shaped. The two dimensional high definition image input device with the squared pixels are expensive due to less demand. By contrast, a large number of the image sensors for the high definition television system are required thereby a cost of each of the image sensor may be reduced. For that reason, it is required to develop an image sensor being available for both the high definition television system and the computers. This further permit peripheral devices to be used commonly. Furthermore, it is permitted that any software developed for the high definition television system may be available to the computer and printing fields.
In the view point of common use of the image sensor in the high definition television and the computer, it was proposed that the high definition television system image sensor with the rectangular-shaped pixels picks up the image for computer processing. In this case, the image signals are required to be converted into analog signals for sampling at the predetermined frequency and subsequent conversion of digital signals for the square pixels. This analog to digital signal conversion may result in a deterioration of signal-to-noise ratio. Beat with the sampling frequency may permit a periodic noise generation. An expensive high speed analog-to-digital converter is required thereby resulting in an increase of the cost of the device.
Other two ways were proposed in which the image is picked up by the image sensor with the squared pixels available for computers to be displayed on a screen of the high definition television system. A first way is to keep the number of scanning lines but vary the number of pixels aligned in the horizontal direction. In case of the solid state image sensor with 2,000,000 pixels in one inch formal, unit pixels are designed to have the squared definition of 7.3 micrometers and 7.3 micrometers while normally the vertical and horizontal sizes of the unit pixels are 7.6 micrometers and 7.3 micrometers respectively in use for the high definition television system. When the squared pixels are aligned in the active image area of the vertical to horizontal ratio of 9:16, then a reduced number of pixels may be permitted to be aligned within he active image area, thereby resulting in a lowering of the reading out frequency for the image signals.
To raise the reading out frequency, it is required to newly design the driving circuit and the image signal processor involved in the image sensor. This is not preferable in view of the high definition television regulation.
A second way is to design the squared unit pixels to have size of 7.3 micrometers.times.7.3 micrometers so that the number of the active squared pixels is increased from 1036 up to 1080. As illustrated in FIG. 3, 1080.times.1920 pixels are aligned in the active image area. Notwithstanding, the number of the pixels aligned in the horizontal direction is not changed. Hence, the reading out frequency for the image signal is the same as that of the 2,000,000 pixels.
In electing the second way, when displaying the image signals on the monitor screen with 1036 active scanning lines for the high definition television system. Then as illustrated in FIG. 3 the image displayed on the screen is extended by 45 in the vertical direction and further on the screen non-displaying areas including 44 scanning lines are present. Normally, acceptable image distortion is within 3% so that the image distortion may be compensated by 4% lowering of a triangle waveform voltage to be applied to a vertical deflecting yoke of the cathode ray tube.
Otherwise, a vertical sweeping time is compensated to be extended by 4% so that 1080 scanning lines may be displayed on the screen thereby as illustrated in FIG. 3, the image picked up by the image sensor with the square pixels may be completely displayed on the high definition television screen of 9:16 without any lack of the image or any image distortion. Notwithstanding, this way requires a judgment of whether the image signals are picked up by the rectangular-shaped pixels of the high definition television image sensor or by the squared pixels image sensor and subsequent switching operation so the vertical sweeping voltage and the sweeping time. Actually, it is difficult to judge whether the image displayed on the screen has the 4% image distortion. In the above viewpoints, it has been required to develop a novel display device.